Bio 201A
Terms
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- Graph of two characters and their fitnesses
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Adaptive landscape
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(Incorrect) idea that offspring are literal phenotypic blends of parents (like an average)
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Blending inheritance
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Change in gene frequency due to mutation;
Equilbrium frequency;
Selection against mutation
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Deltap = -mu p - (1 - p) v
phat = v/(mu + v)
qhat = rt(mu/s)
- Additive fitness: each allele adds the same amount of fitness benefit per genotypic appearance
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Codominant allele
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Alternative equilibria
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Positive frequency-dependent selection, heterozygous disadvantage
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An alternative state of a particular gene at a locus
- Allele
- an ensemble of small populations, often exchanging gene flow; example
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Metapopulation; less Swedish butterflies as you moved away
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Average heterozygosity of a population
- H = sum(# heterozygotes at each locus)/(100*n)
- Birds and mammals have a cline such that larger animals occur in the north
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Bergman's Rule
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Broad-sense heritability
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VG/VP
Proportion of phenotypic variation which is genetic
- Chance change sin allele frequencies
- Genetic drift
- Change in frequency in alleles for selection for a recessive allele
- Delta q = spq^2/(1+sq^2)
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Change in one generation due to selection
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zbar = Beta * VA = R = h^2*s
- Coefficient of relatedness
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Probability of a gene shared by two individuals being identical by descent; r= sum ((1/2)^L)
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Coefficient of Variation
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CV=S/xbar
Allows for comparison of deviaitons between different groups
- Conditions/equation for HArdy-Weinberg Equilibrium
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1. Random Mating
2. Infinitely large population
3. No natural selection
4. No mutation
5. No migration
p^2 + pq + q^2 = 1, where
p = f(A), q = f(a), etc.
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Continent island model of migration
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pI* = (1 - m) pI + m pC
Deltap = m(pC - pI)
Delta pI = -s pI qI^2/(1 - s + s qI^2) (for selection against p)
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Contribution of a genotype to the next generation
- Fitness
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Convergent evolution
- Pattern of having similar phenotypes evolve repeatedly in distantly related lineages; mammals and marsupials, pangalins and armadillos
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Copy of a gene made on one chromosome due to improper crossing over
- Duplication
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Correlation coefficient
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rxy = sum(xbar -x) (ybar - y)/(N Sx Sy)
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Detection selection
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No equilibrium, phenotypic correlations (Bergman's rule), Survivors v. non-survivors (intemrediate galls win), functional studies (notothenoid enzymes), convergent evolution, molecular methods (DNA tests,statistics to look at positive selection)
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Directional selection
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Shifts mean; insecticide resistance
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Disruptive selection
- Mean same, variance increases; blacb-bellied seed crackers with extreme bills
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Effective population size
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- Ne (as opposed to Nt)
- Variation in fecundity (elephant seals - female hogging)
- Uneven sex ratio (wasps and mites - female favored)
- OVerlapping generations
- Population size fluctuation (cheetah bottlene
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Effects of genetic drift
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- evolution without selection
- Loss of variation in a population
- Increase in variation between populations
- Probability of an allele becoming fixed = frequency of allele right now
- Faster in smaller popula
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elaborate ornaments are a handicap, so must have good genes to back it up
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Handicap hypothesis
- Equation for genetic variation
- VG = VA +VD
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Equation for Phenotypic Variance
- VP =VG + VE
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Everyone breeds equally and has equal fertility
- Ideal Population
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Everything on one side of the divide dies
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Truncation selection
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Evolution of female choice
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- Direct benefit (nuptial gifts, territory)
- No direct benefit (leks)
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Example of evolution
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Selecting for drug-resitant bacteria
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Examples of altruism
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Ground squirrel warnings; pied kingfishers helping at the nest (PH>SH>Delay - sexy helpers)
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External characteristics of an individual as afffected by genotype and environment
- Phenotype
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Females selecting for certain males get better offspring
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Good genes hypothesis (peacock eyes)
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Fluctuating selection
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Temporal: Finch beaks and seed size changes with rain
Spatial: Flowers in a patchy field
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Frequency of an allele changes because of association with another, selected allele
- Indirect selection
- Gene flow example
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Banded water snakes - still intermediates on the island despite selection for unbanded snakes
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Gradual change in allele frequency or in the mean of character ove ra geographic transect; example
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Cline; AP94 for salinity in Long Island Sound mussels; copper tolerance in grass near mines
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Hamilton's Rule
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An altruistic trait will evolve when B*r - C > 0
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Heterozygous advantage
- Overdominance; sickle cell allele
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Heterozygous disadvantage
- Underdominance; mutations more common in heterozygotes, balance favors more common allele
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History of evolutionary theory
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Plato: Ideal types
Aristotle: Scale of life
Ray: Natural complexity reflects God's thought
Linnaeus: As many species now as God first made
Agassiz: World not static
Buffon: Animals occaisionally altered into new specie
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Inclusive fitness
- Direct and indirect selection; fitness through whether or not blood relatives reproduce
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Infinite number of character states
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Continuous Traits
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Inverse frequency-dependent selection
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Rarer alleles favored; search image predation in fish
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Kin selection
- Promotes aid or assistance between individuals and descendent or non-descendant kin
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Lamark v. Darwin
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Lamark: Inheritance of acquired traits
Darwin: Evolution through natural selection
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Less parasites = better ornaments
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Parasite hypothesis; mite of the swallow tail length
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Maintenance of polymorphisms
- <>Fluctuating selection, Inverse frequency-dependent seleciton, Heterozygous advantage (overdominance)
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Males with higher trait values carry alleles for female preference
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Arbitrary male hypothesis
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Mating systems
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Monogamy, polygamy
- MHC alleles example
- Najor Histocmpatibility Loci genotypic frequencis in Hasupai Native Americans not in equilibrium, either due to more miscarraiges for share dMHC alleles or non-random selection of unlike MHCs
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Mutational speed experiment
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E. Coli
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Narrow-sense heritability
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h^2 = VA/VP
Proportion of phenotypic variablity due to additive genetic inheritance (proportion which is heritable/responsive to evolution
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Negates induced mutation idea
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4 cultures, 4 incubators; tree distribution for mutations
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Net Fitness
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Survival Fitness * Average fecundity
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New population founded by a small number of colonists; example
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Founder effect; old order Amish
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Operational sex ratio
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Ratio of available males to available females; skewed towards males (more effort for females)
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pair bonds
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Monogamy (birds); shrimp
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Physical location of a gene
- Locus
- Polygamy
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- Polygyny: Males mate with many females; scramble competition (male race - horseshoe crabs), female defense (bats), resource defense (impalas), lek (male display territory - Uganda kobs)
- Polyandry (Jacanas - males take eggs)
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- Postiive frequency-dependent selection
- most common allele favored; warning coloration
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Response to selection
- R = h^2 *S
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Selection differential
- S = (t* - tbar), where t* is the mean of the trait before selection
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Selection gradient
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Slope of the regression of relative fitness on the character = Beta
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Selection vs. drift dominance
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Ne s >>1 vs. Ne s <<1
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Set of genes belonging to an individual
- Genotype
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Stabilizing seleciton
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Mean same, variance lower; birth weight
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Standard deviation
- S=rt(V)
- Theory of evolution by natural selection
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1. Traits need to show variation
2. Some variation must be heritable
3. Individuals must differ in fitness
4. There must be a correlation between phenotype and fitness
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Three modes of selection
- Directional, Stabilizing, Disruptive
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Traits that have a finite number of character types
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Discrete Traits
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Transition vs. Transversion
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Purine to purine, purine to pyramidine
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Types of mutation by effect
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- Apomorphic - none
- Hypomorphic - reduced fxn
- Hypemorphic - increased fxn (usually dominant)
- Xenomorphic - different fxn
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Unit on a chromosome that encodes for one protein
- Gene
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Units of selection
- Individual, Genes (meiotic drive - house mouse t locus), organelles (fast dead red mitchondria mutant in fungus), cells (cancer), group selection (flour weevils, viruses and hosts, species (snails overrespresenting), kin selection
- Variance
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V = sum(xbar - x)^2/n